Process and apparatus for making curled thermoplastic yarn



Aug, 23, 1960 P. VAN DIJK I 2,949,721

PROCESS AND APPARATUS FOR MAKING CURLED THERMOPLASTIC YARN Filed June 6, 1955 2 Sheets-Sheet 1 INVENT OR ATTORNEYS R. VAN DIJK Aug. 23, 1960 PROCESS AND APPARATUS FOR MAKING CURLED THERMOPLASTIC YARN 2 Sheets-Sheet 2 Filed June 6,' 1955 IINVENTOR I Fidel vanfl i lk dam, %M; aw

ATTORNEYS PROCESS AND APPARATUS FOR MAKING CURLED THERMOPLASTIC YARN Pieter van Dijk, Velp, Netherlands, assignor, by mesne assignments, to American Erika Corporation, Enka, N.C., a corporation of Delaware Filed June 6, 1955, Ser. No. 513,442

(Ilaims priority, application Netherlands June 17, 1954 7 Claims. (Cl. 57-34) This invention relates to the curling of synthetic thermoplastic threads or yarns and more particularly to an improved method and apparatus for the continuous production of curled yarns or threads of high uniformity and excellent appearance.

It is known to curl thermoplastic yarns by imparting a false twist to them, gas heating and cooling them while they are twisted, and then untwisting. Due to the thermoplastic nature of the yarns, the application of heat to them while they are twisted makes the curl permanent. However, with known methods and devices for curling thermoplastic yarn, the product is characterized by lack of uniformity in appearance and lack of uniformity in elastic properties. It has been known that the undesirable properties come from non-uniform heating and much of the prior art effort has been devoted toward trying to achieve a more uniform transfer of heat from the hot gas to the thread. Any type of heat exchange surface that was tried in the prior art resulted either in stopping the twist or in inadequate uniformity of heat exchange.

It is an object of the present invention to overcome the difiiculties of the prior art and to provide a method and apparatus for curling thermoplastic yarn having desirable elastic properties apparent in knit goods manufactured therefrom, uniform surfaces and good stitchforming characteristics. Furthermore, according to the present invention, a curled product is obtained in which the uniformity of the elastic properties is very stable.

It is proposed as a part of this invention to heat the twisted yarn by contact with a metal surface under conditions which do not stop the twist or interpose irregulan'ties and yet which promote a high uniformity of heat exchange.

Other objects and advantages of the present invention will be apparent upon consideration of the following detailed description of several embodiments thereof in conjunction with the annexed drawings wherein:

Figure 1 is a diagrammatic view of a continuous curling unit constructed in accordance with the teachings of the present invention;

Figure 2 is a view of the tension control apparatus of Figure 1;

Figure 3 is a view in vertical section of the false twister;

Figure 4 is a perspective view, partly broken away, showing the preferred type of heater in accordance with the present invention; and

Figure 5 is a fragmentary view of a less preferable form of heater in accordance with the present invention.

In Figure 1 the numeral indicates a thread package from which the thread 11 is withdrawn to be subjected to the curling operation. The thread passes through guides 12 and 13 and then through a fork 14. The fork 14 guides the thread for movement between two frustoconical supply rollers 15 and 16. After leaving the supply rollers 15 and 16, the thread passes between tenatent C ice sioning gears or toothed wheels 17 and 18 over the heater 19, through a free air cooling space 20 and into the false twister 21. The thread leaves the false twister at port 22, forms a balloon, the upper end of which passes through a guide 23. After leaving the guide 23, the thread passes over a draw-off godet 24, around a guide wheel 25, through a thread guide 26 to a point of collection 27.- The gears 17 and 18 impart tension to the thread and also act as a twist stop at one end of the false twist path and, at the other end, the godet 24 similarly functions as a twist stop. Thus between gears 17 and 18 and port 22 the false twist is placed in the thread and between port 22 and godet 24 it is taken out.

If now reference is made to Figure 2, it can be seen that the thread approaching the frusto-conical rollers 15 and 16 passes through the inclined tines of fork 14. The vertical position of the fork 14 varies in response to the tension of the thread. To this end the fork is made integral with a balanced lever 28 which is pivoted at 29 and which carries at its other end the toothed wheels 17 and 18. Rocking movement of the lever 28 about the pivot 29 is controlled by the tension in the thread and weights 31, and is dampened by the fluid in receptacle 30 and a cooperating paddle. which is integral with said lever. It can now be seen that if the thread tension becomes excessively high due to shrinkage in the heating, or fixa= tion, zone the effect is to move the thread to the left of the Figure 2 position to increase the effective peripheral speed of the supply rollers 15 and 16. Similarly, if the tension in the thread at the heater decreases the effect of the weights 31 on the lever 28 is to move the fork 14 upwardly to shift the thread to the right from the Figure 2 position thereby to decrease the effective peripheral speed of the conical rollers 15 and 16. In other words, when the thread engages a large diameter portion of these hollers, the supply rate is high and when it engages a small diameter portion the supply rate is low;

The heater 19 is in the form of awire, rod or bar having electric resistance elements embedded therein. The bar is supported by a bracket 32. Thermostat 33 meas' ures the temperature of the bar and controls the circuit of the heater 19 in a manner to maintain the temperature at a predetermined value. The thermostat and heating controls per se are known to the art and form no part of the present invention. I

The false twister 21 is supported from a bracket" 34 and its head 35- is mounted for rotation with a hollow spindle 36. The head 35 is connected by a belt 37 to the sheave 38 of a motor 39. The head 35 is provided with a storage wheel 40 and a ballooning guide 41. The general construction of the false twister is in conformity with the disclosure of application Serial No. 442,166, filed July 8, 1954, which is commonly owned herewith.

While the heater 19 is shown exposed in Figure l, in order to conserve heat, it is actually, in practice, covered by a hood 42 held by spring clips 43 from the support 32, all as can be easily seen in Figure 4-.

.It has been found that to assure good contact between the thread 11 andthe heater 19 while avoiding atwi'st stop effect, the thread should helically surround the rod portions thereof for about 360 at a helix angle, or angle of inclination with respect to a plane normal to the longitudinal axis of said rod, of at least 70.

For the heating of polyamide threads of 30-70 denier moving with a speed of 15-18 meters per minute, a heater 19 having a resistance rod with a length of a little over 70 millimeters is satisfactory. For threads moving with-a higher speed and having higher deniers, resistance-rods of a length of slightly more than millimeters are sufiicient.

Experience has shown that no twist stop occurs if the thread is passed over a smooth cylinder with an encircling angle of measured in a direction perpendicular to the cylinder axis. This information should be utilized in determining dimensions of the heater 19.

To prevent twist stop in a thread moving along a helical line having an angle of inclination of 70 with the cylinder axis, the diameter of the cylinder used should be about 125 millimeters with a length of contact of 140 millimeters. The angle of encircling is then 45. With an angle of inclination of 80 a cylinder of about 32 millimeters will be sufficient, the angle of encircling being about 86. With angles of inclination of 88, 8830 and 89 heating bodies with diameters of 1.2, 0.6 and 0.2 millimeters respectively may be used, the respective angles of encircling being 430, 570 and 860.

The data presented above naturally give only an impression of the possibilities within the scope of the invention. By no means is a restriction implied thereby.

Thus it is, for example, not necessary to apply the maximum allowable encircling in the case of greater angles of inclination. When using a resistance rod with a diameter of 1 millimeter and an operative length of 140 millimeters, the heater being heated at 160l70 C. whilst the angle of encircling is adjusted to 360 and the angle of inclination of the helical line at 8830", the heating is satisfactory to fix the twist in the case of polyamide threads of 70 denier and higher which threads are moved over the wire rod with a speed of 25-30 meters per minute.

With the device according to the invention it is possible to maintain the tension in the fixation zone, or heater 19, at about 0.5 g. for 30/ 10 and 30/6 threads, whereas for a 50/ 10 thread the tension may be kept at about 1 g. With a 70/ 18 thread it was found that a tension of about 1.5 g. is satisfactory. When tensions are too high irregularities occur in the curled thread. The tension to be used is accurately adjusted by means of weights 31 on the balance lever 28. These weights in effect determine the drag imparted to the thread by rollers 17, 18.

The false twisting device 21 is driven at a high speed and with a 30/10 thread a speed of e.g. 54,000 rpm. was used. The speed of supply amounted to 17.4 meters per minute. The length of the hollow spindle 36 of the false twisting device 21 was 73 millimeters and the diameter of its bore 0.6-0.7 millimeter. A practically vibration free passage of the thread over the electrically heated resistance rod was obtained because of the fact that the thread leaves the false twisting device 21 in a ballooning manner and by the given dimensions of the hollow spindle and diameter thereof. The temperature .of the heated surface is generally kept between 160 and 170" C. The cooling zone after the heater 19 is generally kept at a length about equal to that of the heated surface.

While the passage of yarn or thread around a polished surface of a heater rod in a generally helical path is the most desirable way of setting the curl, it is possible to use other curved polished metallic surfaces. An example of one of these is shown in Figure 5. In that case, the heater 44 is a metal block heated with resistance elements and maintained at a desired temperature by a thermostat 45. The block presents a surface at 46 which may be curved on a radius of about 360 millimeters.

The temperature of the block 44, or indeed of the heater 19, is maintained within about one degree Centigrade from the predetermined value set on the thermostat. Instead of heating the rod of heater 19 electrically, that rod may be hollow and a heating medium such as steam or another fluid may be passed therethrough.

Instead of a collecting device as shown which is in the form of a winding device, the finished curled thread or yarn may be collected on a twist spindle. in that case, the newly applied twist preferably is opposite to the direction of the false twist remaining in the thread after heat setting.

Throughout this specification and the appended claims the terms thread and yarn are intended to be used interchangeably, it being apparent that the invention is equally applicable to both.

What is claimed is:

1. Apparatus for imparting a uniform curl to thermoplastic yarn comprising a tensioning device, a false twisting device, means located between said devices for pre senting a smooth heated metal surface to the yarn, means for withdrawing the yarn from said false twisting device at a predetermined rate, supply means for feeding yarn to said tensioning device at a variable rate and means responsive to variation in tension in the running yarn for controlling the feed rate of said supply means, said last named means including a lever pivoted intermediate the ends thereof for supporting said tensioning device.

2. Apparatus for imparting a uniform curl to thermoplastic yarn comprising a tensioning device, a false twisting device, means located between said devices for presenting a heated metal surface to the yarn, means for withdrawing the yarn from said false twisting device at a predetermined rate, supply means for feeding yarn to said tensioning device at a variable rate and means responsive to variation in tension in the running yarn for controlling the feed rate of said supply means, said heated metal surface being curved and offset in relation to a straight line between said tensioning and false twisting devices and said tension responsive means including a lever pivoted intermediate the ends thereof for supporitng said tensioning device.

3. Apparatus for imparting a uniform curl to thermoplastic yarn comprising a tensioning device, a false twisting device, means located between said devices for presenting a heated metal surface to the yarn, means for withdrawing the yarn from said false twisting device at a predetermined rate, supply means for feeding yarn to said tensioning device at a variable rate and means responsive to variation in tension in the running yarn for controlling the feed rate of said supply means, said heated metal surface being the surface of a rod around which the yarn passes in a spiral path at a helix angle of at least 70, and said last named means including a lever pivoted intermediate the ends thereof for supporting said tensioning device.

4. Apparatus as claimed in claim 3 wherein the rod has an electric resistance therein for heating the same.

5. Apparatus for imparting a uniform curl to thermoplastic yarn comprising displaceable tensioning rollers, a false twister, a heating surface located between said tensioning rollers and said false twister, draw-off means for withdrawing yarn from said false twister at a predetermined rate, frusto-conical supply rollers for feeding yarn to the tensioning rollers at variable rates and means responsive to displacement of said tensioning rollers for shifting the yarn laterally along the surface of said frustoconical supply rollers for controlling the feed rate there of, said last named means including a lever pivoted intermediate said heating surface and said supply rollers for supporting said tensioning rollers at one end thereof and having a thread guiding fork formed on the other end adjacent said supply rollers.

6. Apparatus for imparting a uniform curl to thermoplastic yarn comprising tensioning rollers, 21 false twister, a heating surface located between said tensioning rollers and said false twister, draw-off means for withdrawing yarn from said false twister at a predetermined rate, frusto-conical supply rollers for feeding yarn to the tensioning rollers at variable rates and means responsive to variation in tension in the running yarn for controlling the feed rate of said supply rollers, said tension responsive means comprising a lever pivoted intermediate the ends thereof, means in one end of the lever for rotatably supporting said tensioning rollers, an inclined yarn guiding fork fixed on the opposite end of said lever and adjacent the supply rollers and damping means for minimizing oscillation of said lever.

7. A process for imparting a uniform curl to thermoplastic yarn comprising the steps of supplying yarn at a variable rate from a supply source to a fixation zone, tensioning said yarn between said supply source and said fixation zone, imparting a false twist to the yarn passing through said fixation zone, heating the yarn in said fixation zone while maintaining the same in twisted condition, withdrawing the yarn from said fixation zone at a predetermined rate while allowing the same to cool, and

varying the rate of supply into said fixation zone in response to non-uniformity of shrinkage resulting from said heating, whereby the yarn tension will be maintained constant throughout the fixation zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,345,032 Castricum Mar. 28, 1944 2,761,272 Vandamme et a1. Sept. 4, 1956 FOREIGN PATENTS- 145,419 Australia Feb. 26, 1952 1,072,786 France Mar. 17, 1954 1,074,322 France Mar. 31, 1954 

